London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

Terrorists who want to harm the UK are "waiting for the moment when we take our eye off the ball", the Security Minister has said.

The emergency services need to be better prepared to tackle a lone gunman on the streets of Britain and the UK is facing an increasing risk of terrorism from the situation in Mali, James Brokenshire said.

"A collective failure to act might well manifest in attacks closer to home," he said. "Those who want to do us harm are waiting for the moment when we take our eye off the ball. The threat remains very real. But that does not mean we cannot stay ahead of it."

Home Secretary Theresa May has asked the police and other emergency services "to make further improvements to the joint response", he added.

Speaking at the Royal United Services Institute (Rusi) in London, Mr Brokenshire said: "Staying ahead of the threat means ensuring our emergency response is capable of dealing with the threat in whatever form it takes.

Changing tactics have allowed terrorists to "achieve a devastating effect using relatively unsophisticated means", he added.

"The experiences in Toulouse and in Norway demonstrate the impact that a lone individual can have if sufficiently motivated, while the November 2008 terrorist attacks in Mumbai were characterised by an ongoing firearms and explosives attack, and by hostage-taking. So we are improving the way the emergency services work together in response to a major incident."

Lone individuals sympathetic to al Qaida's cause were believed to have been one of the major concerns of the security services and police in the run-up to the Olympic Games.

Mohamed Merah, who said he had links with al Qaida, killed seven people in France's worst terror attacks in years near Toulouse in March, while Anders Breivik went on the rampage in Norway, killing 69 people in July last year. And in 2008, 166 people were killed in the Mumbai terror attacks.

Marie Staunton, chief executive of international children's charity Plan UK, said: "The Malian crisis is a global threat which could, unfortunately, persist for years. If this situation is allowed to stand, the area will become a hub for sponsoring terrorism, regionally and globally. The world must not stand by while this happens."